1. Field of the Invention
The present invention relates to a method and apparatus for controlling the air-fuel ratio in an internal-combustion engine.
2. Description of the Prior Art
Generally, in an internal-combustion engine of an electric fuel-injection (EFI) type, during the start of the engine and immediately thereafter, the intake-air amount is so small that it cannot be detected by an airflow meter. As a result, the fuel-injection amount is controlled by the fuel-injection pulse duration dependent upon only the coolant temperature of the engine. In this case, not that such a fuel-injection pulse duration is predetermined on the condition that the accelerator is not operated, i.e., the throttle value is completely closed.
In the above-mentioned engine, however, if the driver operates the accelerator during the start of the engine or immediately thereafter, the intake-air amount is changed in response to the change of the opening of the throttle valve so that the air-fuel ratio is changed. The position of the accelerator during the start of the engine and immediately thereafter is often changed by the driver since the driver operates the accelerator in an internal-combustion engine of a carburetor-type. Therefore, if the air-fuel ratio matches the condition of the accelerator not being operated, operation of the accelerator makes the air-fuel mixture lean and, accordingly, engine speed may not increase as desired and the phenomenon of backfiring may occur. Contrary to this, if the air-fuel ratio matches the condition of the accelerator being operated, non-operation of the accelerator makes the air-fuel mixture rich and, accordingly, the plugs may smoke.